Inside Nick Reiner’s sheltered Hollywood upbringing and how he left mum ‘at her wits end’ before grisly double murder

The cold-blooded murder of Rob Reiner and wife Michele Singer Reiner, their throats slit as they slept on Dec. 14, is one of the most heartbreaking Hollywood crimes of the modern era.

Nick, 32, had allegedly decamped to a hotel where he left a room soaked in blood, but was arrested by cops that night, while his siblings Romy, 28, Jake, 34, and half-sister Tracy, 61 — Rob’s adopted daughter with his first wife — started trying to piece together what happened.

By all accounts, Nick was different to his well-adjusted siblings. The Reiners are Hollywood royalty, with grandfather Carl Reiner a pioneering TV comedian and director and Rob the director of classics including “Stand by Me” and “When Harry Met Sally,” so the kids grew up with the privileges of princes and princesses.

However, Nick had struggled with drugs since his teenage years, been in an out of rehabs, spent spells homeless and, according to a report Friday by TMZ.com, had recently been diagnosed with schizophrenia.

“As a kid, Nick always needed more attention [than the others],” said one NY Post source close to the family.

“He would throw fits” — which later included punching walls; on at least one occasion, he wrecked a TV and lamp.

“He was a very hyper little boy. They always had to keep an extra eye on him,” the source said.

“He wasn’t stable. There were many times when Nick had a rant and it affected everyone … Michele would say to people ‘Please don’t upset him.’ The family and all their helpers would basically cater to him. The rule was always ‘Give him what he wants.’”

Romy and Jake, who are both now involved in the movie business, did all that they could to pitch in. As children, the source said, “they helped him. [They would] keep him entertained and calm.”

After some of his most tumultuous years, Nick seemed to be getting things together around 2014 when he and his father started work on “Being Charlie,” a semi-autobiographical movie about a teen’s drug addiction and his relationship with his super-famous father.

Barry Markowitz, the cinematographer who shot “Being Charlie,” which Rob directed and Nick co-wrote, was a frequent guest at the family’s home.

“I saw nothing but love,” he told The Post, recalling how he spent his time shooting baskets on the home’s court.

He also did what he could to boost Nick: “I’d talk to him and ask him for advice, out of respect.”

He said there was plenty of love to go around in the Reiner household, and Nick’s siblings did not resent him for requiring more attention than they did.

“There was never any hint to my eyes of resentment,” said Markowitz, who also remembered how the walls alongside the staircase were loaded with family photos.

He said the attitude was more like “Let’s keep trying. Let’s keep on not giving up. You have hope and you never give up. They were one team.”

The movie, released in 2016, received lacklustre reviews and didn’t make much of a dent in Hollywood, and Nick quickly went back to his old ways.

Nick had at least 18 stints of rehab, but hated going, so Rob and Michele hired sober coaches to help out. He had lived in their guesthouse for around the last five years, according to reports.

“There were months when Nick would be okay,” said the family source. “He isolated himself in the guest home, he was quiet. He went on and off [drugs]

“Then all of a sudden he would go downhill. They would get personal coaches to help him out, instead of putting him in an institution.

“They felt like he did better when the coaches came in. But then Nick would get upset that the coaches were there and [the Reiners] would fire them.”

Sources said there were never any signs Nick would do anything violent, as happened on December 13, and if his parents had feared him “they could have locked him out of the main house if they were worried,” but that’s something that wasn’t in their character to do.

TMZ claimed Nick had been diagnosed with schizophrenia just weeks before the murders and medication he took for the condition made him “erratic and dangerous,” with a source claiming, “Nick was out of his head.”

The Post’s sources said that seemed exaggerated. They claimed while Nick had ditched his healthy diet, usually a sign he was using drugs again, he had also lost weight. But they had not known him to get violent.

However, in recent months he was “not acting like himself” and it had left Michele “at her wits end,” sources said.

In fact, the sources said it was something of an anomaly for Nick to go to a party with his parents, as usually he would shrug such things off, but they would have been glad he wanted to socialise.

“They wanted to include him. They wanted to get him involved in as many things as possible,” the source added.

However, once at Conan’s party, things didn’t go smoothly, with Nick causing scenes.

“They had had an argument at Conan’s holiday party, and Rob had been telling people that they’re scared for Nick and scared that his mental state was deteriorating,’’ a lifelong family friend who lives near the Reiner home told The Post this week.

He also had an altercation with “Barry” actor Bill Hader, interrupting a conversation he was having, concerning other guests.

According to other reports Friday Nick’s behaviour was disruptive enough, at least one person threatened to call the authorities.

“But Conan stepped in and said, ‘It’s my house, my party, I’m not calling the police.’ He talked them out of calling the police,” a source told the Daily Mail.

By Wednesday, Nick wore a vacant stare and a blue suicide vest as he was hauled into the dock. He did not enter a plea and only uttered “Yes, your honour” when asked if he waived his right to a speedy arraignment.

His fate will play out in the legal system, but while he awaits his fate, the remaining members of his family have an unimaginable task in front of them to face the world without their parents. Yet they still hinted at compassion for their brother in the joint statement Romy and Jake released. "Words cannot even begin to describe the unimaginable pain we are experiencing every moment of the day … we ask for respect and privacy, for speculation to be tempered with compassion and humanity, and for our parents to be remembered for the incredible lives they lived and the love they gave,” it read.